The value of Bulk modulus is not very large (15.3120 GPa), which is less
than standard value of 40 GPa to specify any material a superhard
[37]. While value of Young’s modulus (37.2189 GPa) specifies that
LiBH4 is a stiffer compound. If value of the Pugh’s
criteria [36] \(\frac{B}{G}\) >1.75 the material is
said to be ductile else brittle. In our case \(\frac{B}{G}\) is less
than 1.75, thereby, declaring LiBH4 a brittle material.
Moreover, if \(\nu\) < 0.26 the material is deemed brittle
else ductile [38], which is less than 0.26 for LiBH4so it endorses its brittleness. If the value of an anisotropic factor
(A) is equal to unity, the material is isotropic else anisotropic
[39-40]. In our case, the value of anisotropic factor is less than
unity for LiBH4 which indicates its anisotropic
behavior.
- Optical Properties
- Dielectric function
Dielectric function is deemed to be an important parameter, which is
capable of illustrating the polarizability and energy loss function of
any material. Particularly, its real part describes polarization of the
materials, since dielectric function can be split into two parts; the
real and imaginary parts which are drawn as a function of frequency and
shown in figure 9. The complex dielectric function can be expressed
through well-recognized Kramer-Kronig [32-41] relation as given
below:
ℇ(ω) = ℇ1(ω) + i ℇ2(ω) (1)
Other than the dielectric function, we have also investigated frequency
dependent energy loss function, refractive index, optical conductivity
and reflectivity. Dielectric response of the material is mainly
associated with the multiferroicity [42]. Penn’s
model can be expressed as [43]:
\(\varepsilon_{1}\left(0\right)=1+\left(\hslash\frac{\omega_{p}}{E_{g}}\right)^{2}\)(2)
In this relation \(E_{g}\) is energy gap and\(\ \omega_{p}\) is the
plasma frequency.